The consumption of food items that are attached to or embedded within substrates places very different demands on jaw structures than the consumption of foods that are suspended within the water column. Most research into fish jaw functional mechanics has focused on the latter, leading to generalized models of fish feeding biomechanics that have little relevance to highly specialized surface-scraping fishes like loricariid catfishes. To remedy this, and to understand how loricariids' diverse jaw
morphologies might relate to diversity of function, I developed a novel
loricariid jaw model. This model is built from a set of morphometrics that can be measured on disarticulated bones, allowing morphological
differences in preserved specimens to be linked to ecological differences that may have shaped evolutionary diversification. Other recent research has examined the convergent specializations of rheophilic fishes.
EXAMPLE 1: Lujan, N.K. and J.W. Armbruster. 2012. Morphological and functional diversity of the mandible in suckermouth armored catfishes (Siluriformes: Loricariidae). Journal of Morphology 273:24–39.
This study used the jaw model above to investigate jaw functional diversity across 25 Loricariidae species and 12 genera from the middle Marañon River in northern Peru. This study has since been expanded to encompass far more species from a much broader geographic range. Those data are currently being analyzed in an explicitly phylogenetic context (using my recently published molecular phylogeny) and prepared for publication.
EXAMPLE 2: Lujan, N.K. and K. Conway. 2015. Life in the fast lane: a review of rheophily in freshwater fishes. pp. 107–136 in: R. Riesch, M. Plath, M. Tobler, eds. Extremophile Fishes. Springer, Dordrecht.
This review for a recent book on the adaptions of fishes in extreme environments provided the first comprehensive, global summary of fish genera known to be specialized for fast water habitats. It also cataloged the morphological adaptations needed to facilitate station holding, feeding, and reproduction in these habitats.
Fig. 1. Examples of specialized rheophilic fishes from South American rivers. Photo G by L. M. Sousa, all others by NKL.
Fig. 2. Examples of specialized rheophilic fishes from African rivers. Photos by J.P. Sullivan.
EXAMPLE 3: Conway, K.W., N.K. Lujan, J.G. Lundberg, R.L. Mayden and D.S. Siegel. 2012. Microanatomy of the paired-fin pads of ostariophysan fishes (Teleostei: Ostariophysi). Journal of Morphology 273:1127–1149.
We examined the gross morphology and histology of paired-fin modifications (pads) that have convergently evolved in a wide range of benthic ostariophysan fishes. Our examination revealed previously undocumented differences in the cell layers involved in production of the pads, and in the arrangement of unculiferous (keratin producing) cells that line the surfaces of many pads. Scanning electron microscopy of the unculiferous cells of many species revealed rearward-facing, distally hooked projections (illustrated at left) that likely function to both facilitate station-holding while also resisting abrasion from regular close contact with substrates. Loricariid catfishes have their entire bodies and fin rays covered with hypermineralized, rearward-facing teeth called odontodes, which are likely functionally similar in that they protect the fish from abrasion and engage substrate surface irregularities for increased friction during station-holding.